How to make "Himalayan" rock salt chunks in Blender
Ok here is something I made awhile back. It is really involved and maybe overkill. But it is a great learning experience. 

I dont have time now but I will try to update my answer to fill in more details.

Its too shiny but this should get you started.  

I got a lot of tips from this user. 

https://www.blendernation.com/2017/03/23/gemstone-sculpting/

He also did a tutorial on how to do the shader. 

https://www.blendernation.com/2017/03/25/gemstone-shader-breakdown/







Here is the blend file to mess around with



Here is another more simple set up that looks pretty good. 



and this is the Gradient node you will need to build.